This invention relates to a process for etching semiconductor devices, and more particularly to a process for effectively and efficiently etching multi-layer semiconductor devices while maintaining intact the electrical characteristics of these devices.
It is known in the prior art that the manufacture of multi-layer semiconductor devices typically involves patterned etching using liquid or wet etching materials, or dry etching with halogens or halogen-containing compounds, of certain layers which comprise features these devices. For example, one well known etching material is chlorine which can exist in the etching process as either chlorine gas or HCl, etc. Chlorine etches the semiconductor isotropically, i.e., in both a lateral and vertical direction. This results in an etched feature which has a line width which is smaller than the resist image.
Etching can also be conducted in a gas phase using known techniques such as plasma etching, ion beam etching, and reactive ion etching. The use of gas plasma technology provides substantially anisotropic etching using gaseous ions, typically generated by an RF discharge. In gas plasma etching the requisite portion of the surface to be etched is removed by a chemical reaction between the gaseous ions and the subject surface. In the anisotropic process, etching takes place only or primarily in the vertical direction so that feature widths substantially match the photoresist pattern widths.
Although there are many plasma processing modes, as hereinafter described, the two systems that dominate the semiconductor plasma etch field are plasma etching (PE) and reactive ion etching (RIE). For example, in FIG. 1, the major components of a parallel-plate plasma etching system a typical gas plasma etching system 10 are pictorially depicted. The gas plasma etching system 10 includes a gas plasma etching chamber 12 into which a semiconductor device 14 is introduced. An etchant gas mixture is introduced into etching chamber 12 through a gas inlet, described by directional arrow 16, for use in the gas plasma etching of the semiconductor device 14. The chemical species in the plasma are determined by the source gas(es) use. Semiconductor device 14 is located between upper and lower plasma etching electrode plates 22 and 24, respectively. The upper plate 22 is grounded at 26. The lower plate 24 is connected to an RF generator 28 which supplies energy for creating a gas plasma from the etchant gas via the collisions between electrons and gas molecules. It is this gas plasma which etches, preferably anisotropically, semiconductor device 14.
In the plasma etching mode, the electrode areas are symmetrical, and the DC voltage between the plasma and either electrode is substantially the same and relatively small. The various ions and free radicals that are generated in the gas plasma diffuse to the electrode and wafer surfaces where they can react with the material being etched. It is this gas plasma material which anisotropically etches semiconductor device 14 forming a reactive chemical compound. The reaction of the gas plasma with the semiconductor device 14 during a conventional gas plasma etching process forms volatile gaseous by-products. These by-products must be removed from the surface of semiconductor device 14 so that further reaction at the etching site, during the etching process is not inhibited. In order to effectively and efficiently conduct this etching process, volatilization and removal of the volatile by-product must occur. Thus, after the etching operation is completed, substantially all of these volatile gaseous by-products, and any residual etchant gas which may be present, are removed from within the chamber 12 via exhaust system 18. Exhaust system 18 includes an exhaust pump 20.
However, when the above-described plasma etch technology is employed to pattern certain materials which form the various semiconductor layers problems occur. This is because the by-products formed by the plasma etch chemical reaction on the surface of these materials are nonvolatile and cannot be readily removed from these surfaces using conventional plasma etch technology. Many materials, such as copper and cobalt, are therefore not considered for use in VLSI semiconductor fabrication because they do not chemically react to form volatile gaseous by-products. Copper, for example, because of its low resistivity and high level of ductility, would be a highly desirable VLSI semiconductor material, if not for the low volatility of its reaction by-product, particularly its reactive halide by-product.
Therefore, a need exists for a vapor phase etch technology for use with materials which do not readily form volatile gaseous by-products in conventional plasma etching, so that the chemical etching reaction will instead form volatile gaseous by-products which can be readily removed from the surface of the semiconductor device in the vapor phase etching area. The presence of these non-volatile by-product materials on the surface of the semiconductor device inhibits the etching reaction between the etchant gas and the semiconductor device.